The general concept of a step-by-step advancing mechanism is quite old. However, a common problem with known systems is that the step-by-step movement is intermittent and slow. The jacking devices used for causing the movement are operated to cause an increment of movement. Then, such mechanisms must be repositioned while movement is stopped so that they can be used for affecting the next step or increment of movement.
The advancing mechanism of the present invention includes a pair of alternating mechanisms for making step advances. While one of the mechanisms is making a step advance, the other is repositioning itself so that substantially immediately following the step advance it can start making the next step advance. The advancing mechanism of the present invention is especially suitable for use in raising and lowering a platform relative to its support columns.
Mechanisms which exist in the patent literature for raising and lowering platforms relative to support columns are shown by the following U.S. Pat. Nos.: 2,841,961, granted July 8, 1958, to Joseph E. Lucas; 2,892,314, granted June 30, 1959, to John W. Hornsby et al; 2,920,870, granted Jan. 12, 1960, to George E. Suderow; 2,967,400, granted Jan. 10, 1961, to James I. Grant et al; 2,997,852, granted Aug. 29, 1961, to George E. Suderow; 3,028,143, granted Apr. 3, 1962, to David B. Cheskin; 3,082,607, granted Mar. 26, 1963, to John R. Sutton; 3,195,313, granted July 20, 1965, to Edwin P. Swatek; 3,605,669, granted Sept. 20, 1971, to Tsi Van Yu; 3,722,863, granted Mar. 27, 1973, to Isamu Itoh et al; 3,797,256, granted Mar. 19, 1974, to Robert P. Giblon; 3,804,369, granted Apr. 16, 1974, to John R. Sutton; 3,967,458, granted July 6, 1976, to Ralph E. Scales; 3,986,368, granted Oct. 19, 1976, to Clarence W. Levingston; 4,070,868, granted Jan. 31, 1978, to Franz Sedlmayer et al; 4,227,831, granted Oct. 14, 1980, to Darrell L. Evans; 4,255,069, granted Mar. 10, 1981, to Ralph D. Yielding; 4,265,568, granted May 5, 1981, to Robert P. Herrmann et al; 4,270,877, granted June 2, 1981, to Adrianus J. Post; 4,325,654, granted Apr. 20, 1982, to Milton Meckler; and 4,362,120, granted Dec. 7, 1982, to Cornelis Dekkers.